This invention relates to containers; and in particular to food packages having an air impervious liner across the mouth thereof.
Semi-solid food products such as sour cream, whipped butter, cheeses, and various other types of food products are packaged in cupshaped, open mouth, thin-walled containers. A cover having a lip-type rolled edge which engages the rolled rim is used to cover the package. Normally, both the container member and cover are thin-walled (about 0.10 inches thick) and made of a material, such as polystyrene. In the automatic process of producing the packaged food, it was found that in order to close the package the cover must be provided with air vents so as to permit the air entrapped between the food and cover to escape when the cover is pressed onto the container. However it has been found that the venting feature also permits the inflow of air into the package. This inflow of air can provide oxygen for the oxidation or fermentation of the food product.
Various attempts have been made to reduce this possibility of spoilage. One such attempt has included the application of a parchment liner directly onto the top surface of the food product in order to limit to as great extent as possible contact of air with the normally exposed surface of the food; however, the parchment itself is porous, and although to some extent it is effective, nevertheless it is not wholly effective. Another attempt has involved providing a package that includes a container and a cover that carries a heat-sealable plastic liner. In the latter package the cover is pre-assembled with a disc of heat-sealable material adhered to the inner or underside of the cover. This is normally done by applying gobs of hot wax to the inner side of the cover and then overlying the cover and wax with a disc of heat-sealable material. This subassembly (cover and liner) is then mounted to the filled container in the standard manner, but then, in order to completely seal the package the cover and rim of the package are heated so as to cause the plastic liner to adhere to the rim. Although this process is effective to effect a complete seal, the package and its process has a number of disadvantages including the steps of pre-assembly and the heating of the cover to produce the hermetic seal. This heating is communicated through the cover to the food product and this is undesirable particularly when the product is intended to be maintained chilled at all times.
Thus, an object of this invention is to provide an improved package which avoids the problems hereinabove noted, and which characterized by effectiveness without substantial increase in cost. In general the package requires that the liner reduce the amount of air entering the package to a low level; that the liner be substantially inert to automated procedures normally used with thin-walled packages; and that the process by which the liner is applied have no adverse effects on the food product.